High Surf in Hawaii, June 30, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
348 AM HST Sun Jun 30 2019

.SYNOPSIS...
Trade wind weather has returned with more stable conditions over
the western islands. Moderate to breezy trade winds with periods
of windward and mauka showers are expected with drier conditions
over leeward areas through Tuesday. Lighter winds are expected from
Wednesday through Saturday with lower rainfall activity as land
and sea breezes form.

&&

.DISCUSSION...
Satellite imagery this morning shows a weak trough just east of
the state with a stronger disturbance passing well south of the
Big Island. Hawaii doppler radar shows scattered showers drifting
into windward mountain areas with the easterly trade wind flow.
In the upper levels water vapor satellite images continue to show
several lows along an upper level trough north and west of the
island chain. Deeper convective showers remain roughly 100 miles
west of Kauai. More stable air continues to filter in over the
islands from the east today.

Overall a high pressure ridge north of the Hawaiian Islands will
keep a moderate to locally breezy trade winds in place through
Tuesday. Periods of windward and mauka showers are expected mainly
in the overnight and early morning hours as cloud bands ride into
each island with the trade wind flow. Leeward areas will see only
isolated shower coverage. Short and mid range weather models are
in good agreement.

In the longer range forecast the pattern will change starting on
Wednesday and lasting into next weekend. A cold front far north
of the islands will drift south weakening the ridge axis to the
north of the state, and decreasing easterly trades into light east
to southeasterly winds. The weaker large scale winds will allow
local island scale land and sea breezes to develop. Cloud ceilings
will form over island interior sections along with isolated
showers each afternoon. Stability aloft associated with an upper
level ridge will cap cloud heights around 6000 feet for most days
limiting shower activity across the region. Long range models
suggest a brief period of increased showers are possible as a weak
disturbance passes through the eastern islands on Friday.
Otherwise mostly fair weather will prevail across the state.

&&

.AVIATION...
High pressure building to the northeast of the State will maintain
moderate easterly trades for this next 24-hours. Scattered SHRA
will be most concentrated along the windward coasts and slopes,
with isolated -SHRA pushing over onto the leeward sides. Periodic
MVFR conditions will be possible through early this morning due
to mountain obscuration from low clouds and precipitation.

No AIRMETS are currently in effect.

&&

.MARINE...
High pressure northeast of the state will keep moderate to fresh
trade winds in place through Tuesday. The trades are expected to
ease into the light to moderate range during the middle and latter
part of the week as the ridge north of the islands weakens. The
trades may then strengthen back into the moderate to fresh range
next weekend.

A Small Craft Advisory (SCA) remains in effect for the Alenuihaha
Channel and waters south of the Big Island today due to elevated
seas. There is the potential that a disturbance sliding by well
south of the state on Monday could boost winds to SCA levels
across some of the typically windy waters around Maui and the Big
Island.

Spectral density plots from the NOAA buoys south of the state
indicate quite a bit of long-period south-southwest swell energy
heading towards the islands, with some of the nearshore buoys
already registering 3 feet - 20 seconds. The swell is expected to
peak today into tonight, then slowly lower through Monday. As a
result, a High Surf Advisory (HSA) remains in effect for south
facing shores of all islands through Monday afternoon. Additional
southerly swells will keep surf above the summertime average along
south facing shores through the rest of the week. Elsewhere,
expect a modest trade wind swell to continue along east facing
shores through Tuesday, before lowering Wednesday through next
weekend as the trades diminish. North shore surf will remain flat
for the next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai
Leeward-Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central
Valley-Windward Haleakala-Leeward Haleakala-Kona-South Big
Island-Big Island North and East.

Small Craft Advisory until 6 PM HST this evening for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters.

&&

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Jelsema